In general, fire hydrants offer access to a municipal water supply that may be used to control or extinguish fires. Briefly, such fire hydrants include at least one nozzle for coupling to a fire hose. A threaded cap closes off the nozzle when the hydrant is not in use. The hydrant also includes a primary hydrant valve which controls flow of water from the water supply through the hydrant, through the nozzle, and into the fire hose.
Generally, when a hydrant is used to provide water to extinguish fires, or otherwise, a nut on top of the fire hydrant is rotated in one direction to open the primary hydrant valve inside the fire hydrant barrel. Water flows through the hydrant and out the nozzle. When the need for the water no longer exists, the nut is rotated in a second direction closing the primary hydrant valve.
Water may remain in a fire hydrant cavity after the primary valve is closed. Some fire hydrants may provide a drain or drain hole at the base of the hydrant to allow water in the fire hydrant to drain to the exterior of the hydrant. Water must drain from the hydrant to prevent water, in colder climates, from freezing and damaging the hydrant. In some cases, the drain hole may become plugged, thus preventing water from effectively draining from the hydrant. Also, a vacuum may be created inside the barrel of the hydrant that prevents water from draining from the drain hole. Accordingly, a need exists to provide an alternative location to drain at least some of the excess water from the hydrant and/or to equalize the pressure within the hydrant with atmospheric pressure to allow water to effectively drain from the drain hole.
Typically, the barrel of the hydrant between the nozzle and the hydrant valve, which is in the lower portion of the hydrant, accommodates several gallons of fluids or solids. Accordingly, it is possible to unscrew a nozzle cap, introduce gallons of toxin, reattach the nozzle cap, and open the hydrant valve to allow the toxins to communicate with and flow by gravity and perhaps at least to some extent by Bernoulli's principle, into the municipal water supply, since when the nozzle cap is attached, water pressure from the water supply would not force the toxins back out of the hydrant.
An example of a system and method for preventing toxins from being introduced to a water supply through a hydrant is described in U.S. Pat. No. 6,868,860, entitled “Fire Hydrant With Second Valve.” In some examples described in U.S. Pat. No. 6,868,860, a valve structure is introduced between the nozzle and the primary valve that makes it more difficult or impossible to introduce toxins into a water supply through a fire hydrant. The valve structure prevents or substantially prevents the flow of water through the hydrant upon certain conditions and closes off portions of the hydrant barrel when a nozzle is open but the hydrant valve is closed. Generally, the valve structure may include a seat, a restriction member, and a biasing structure.
Hydrants with a secondary valve not only prevent water and toxins from mixing, but also, in some instances, may prevent atmospheric conditions from the barrel above the secondary valve from reaching the area of the barrel below the secondary valve. Since air from the atmosphere does not reach the interior area of the hydrant below the secondary valve, water may not, in some circumstances, drain or weep through the drain hole. Therefore, a need exists for a mechanism that allows water or other liquid to drain out of a fire hydrant when the secondary valve is closed.
Under some conditions, the secondary valve may close when the water level in the hydrant is above the location of the secondary valve, thus trapping water in the upper portion of the hydrant. Under these conditions, the water in the upper portion of the hydrant cannot reach the drain hole located in the lower portion of the hydrant. Allowing water to remain trapped in the upper portion of the hydrant poses a risk of damaging the hydrant in colder climates where the water may freeze. Thus, a need exists for a mechanism that allows water or other liquid trapped above the secondary valve to drain out of a fire hydrant.